Field of the Invention
The present invention relates to an ultrasonic probe suitable for use in an inspection utilizing a photoacoustic effect, and also relates to an inspection apparatus equipped with the ultrasonic probe.
Description of the Related Art
An inspection apparatus capable of obtaining a tomographic image or a three-dimensional image of a sample by utilizing a photoacoustic effect is proposed, for example, as described in U.S. Pat. No. 4,385,634. Such a technique is generally known as PhotoAcoustic Tomography and is called a “PAT technique”.
A process of taking an image by the PAT technique is performed as follows:                1) Light is irradiated to a sample from the exterior.        2) The light propagates inside the sample.        3) The light is absorbed by a portion inside the sample where a light absorption coefficient is large.        4) The portion inside the sample is heated by the light absorption.        5) The heated portion expands.        6) Ultrasonic waves are generated upon the expansion.        7) The ultrasonic waves propagate inside the sample.        8) The propagating ultrasonic waves are received by an ultrasonic probe.        9) A tomographic image or a three-dimensional image of the sample is reconstructed by analyzing, e.g., time differences between the arrived ultrasonic waves.        
Thus, the PAT technique has been so far studied primarily by research institutes in view of advantages resulting from the fact that the technique is based on comparatively simple processing, and that components such as a light source and an ultrasonic probe, which are already used for other purposes, can be employed as they are. In particular, an application to a biological information inspection apparatus for obtaining a high-resolution tomographic image is expected.
However, the PAT technique has the problem that, despite a demand for irradiating light to an inspection target from a position as close as possible to the target, the ultrasonic probe serving as a receiving unit impedes satisfaction of the demand by itself.
To overcome this problem, U.S. Patent Application Publication No. 2005/0004458 proposes an ultrasonic probe 1100 shown in FIG. 11.
In FIG. 11, ultrasonic transducing units (ultrasonic transducers) 1110 are arrayed at a predetermined interval. Optical fibers (light irradiating units) 1120 are disposed in gaps between the ultrasonic transducers 1110 adjacent to each other, and a predetermined light is radiated toward an inspection target from the optical fibers 1120. Ultrasonic waves generated upon absorption of the light by tissues (i.e., light absorbers) inside the inspection target are transduced to an electric signal by the ultrasonic transducers 1110.
Because the ultrasonic probe 1100 proposed in U.S. Patent Application Publication No. 2005/0004458 includes light irradiating regions each formed between ultrasonic receiving regions, an effect of the shade of the ultrasonic probe 1100 can be reduced in comparison with the case of irradiating the light from a position around the ultrasonic probe 1100.
Even with the ultrasonic probe proposed in U.S. Patent Application Publication No. 2005/0004458, however, since the ultrasonic receiving regions and the light irradiating regions are disposed at different positions, a further improvement of sensitivity is demanded, for example, when observing capillary vessels that are positioned in the shallowest portion under the skin of a living body. Also, when the ultrasonic probe having the structure of FIG. 11 is used with a capacitive micromachined ultrasonic transducer (CMUT) using a silicon substrate, which is described in U.S. Pat. No. 5,619,476, it is difficult to fabricate the ultrasonic probe due to the necessity of boring a through hole in the silicon substrate.